As exacerbation of air pollution by large numbers of internal combustion vehicles has become a significant concern in large cities, efforts are being made worldwide to provide efficient electric powered vehicles which do not discharge pollutant emissions. Large cities in developing countries which include high concentrations of scooters powered by two stroke engines are particularly affected by vehicle pollution. These two stroke scooters produce large quantities of pollutants and significant noise. Electric powered scooters, on the other hand, offer a means of transportation that emits substantially no pollutants and produces very little noise.
Electric-powered two-wheeled vehicles have been developed. For instance, U.S. Pat. No. 5,272,938 teaches a bicycle with an electric motor mounted inside a front wheel. The motor is disposed within a housing. The motor spins a sun wheel, which spins three planet wheels meshed therewith. The planet wheels are meshed with and rotate against a ring gear that is rotationally fixed to an axle, which is fixed to the bicycle fork. Shafts of the planet wheels are fixed to a swivel block. The rotation of the planet wheels against the fixed ring gear causes the swivel block to rotate about the axle. Through a clutch wheel, the rotating swivel block rotates the housing. The housing is formed from two halves of equal diameter. Wheel spokes are attached to the housing through both housing halves. Thus, rotation of the housing causes the bicycle spokes and wheel to turn, propelling the bicycle.
In the arrangement taught in the '938 patent, however, the motor is unusually thin to fit unobtrusively within the wheel. This arrangement precludes an ideally shaped motor, which is significantly wider and more powerful.
Other electric powered vehicles are also taught, for example in U.S. Pat. No. 5,322,141. This reference shows an electric motor housed within a closed casing that is connected to a passenger carrying vehicle through suspension members which are pivoted laterally from the vehicle and from the casing. A shock absorber absorbs mechanical shocks between the casing and the vehicle.
The arrangement taught is unsuitable for a scooter or other small vehicles in which swing arms face aft and pivot parallel to the wheel about an axis transverse to the vehicle.
U.S. Pat. Nos. 5,613,569 and 5,647,450 teach electrically powered scooters, each with an electric motor placed in a pivotable swing power unit attached to a main frame and to a wheel. The motor is located at the end of the swing unit attached to the body. As explained in the '569 patent, this placement requires a transmission to provide power to the wheel disposed within the swing unit, such as a belt. The remote placement of the motor from the wheel and the long transmission reduces the potential efficiency of the drive system.
An efficient drive wheel assembly is needed for a scooter suitable for use with an adequately sized motor and which does not suffer from inefficiencies produced by a placement of the motor remotely from the wheel.